Substituted 3-oxo-6-thia-2-azabicyclo [2.2.0] hexanes

ABSTRACT

Disclosed is the antibiotic 5-methyl-2-(1-carboxyl-2-methyl-propen-1-yl)-3-oxo-6-thia-2-azabicyclo [2.2.0] hexane (I): ##STR1## Also disclosed are processes for preparing I and its pharmaceutically acceptable salts and esters; pharmaceutical compositions comprising such compounds; and methods of treatment comprising administering such compounds and compositions when an antibiotic effect is indicated.

BACKGROUND OF THE INVENTION

This invention relates to5-methyl-2-(1-carboxyl-2-methyl-propen-1-yl)-3-oxo-6-thia-2-azabicyclo[2.2.0] hexane (I) and its pharmaceutically acceptable salts and esterswhich are useful as antibiotics: ##STR2## This invention also relates toprocesses for preparing I; pharmaceutical compositions comprising I andmethods of treatment comprising administering I when an antibioticeffect is indicated.

There is a continuing need for new antibiotics. For unfortunately thereis no static effectiveness of any given antibiotic because continuedwide scale usage selectively gives rise to resistant strains ofpathogens. In addition, the known antibiotics suffer from thedisadvantage of being effective only against certain types ofmicroorganisms. Accordingly the search for new antibiotics continues.

Thus, it is an object of the present invention to provide a novelantibiotic and the pharmaceutically acceptable salts and esters thereofwhich are useful in animal and human therapy and in inanimate systems.These antibiotics are active against a broad range of pathogens whichrepresentatively include both gram positive bacteria such as S. aureus,Strep. pyogenes and B. subtilis, and gram negative bacteria such as E.coli, Proteus morganii, Serratia and Klebsiella. Further objects of thisinvention are to provide chemical processes for the preparation of suchantibiotics and their non-toxic pharmaceutically acceptable salts;pharmaceutical compositions comprising such antibiotics; and to providemethods of treatment comprising administering such antibiotics andcompositions when an antibiotic effect is indicated.

DETAILED DESCRIPTION OF THE INVENTION

The compounds of the present invention (I) are prepared according to thefollowing scheme: ##STR3##

In words relative to the above diagram, the starting material 1[R═benzyl; benzyl-6α-bromo-6β-[1-hydroxyethyl] penicillinate; F. DiNinno, et al., J. Org. Chem. 42 2960 (1977)] in a solvent such astetrahydrofuran, diethyl ether, dichloromethane, or the like is treatedwith a triorganophosphine such as triphenylphosphine,tri-n-butylphosphine, hexamethylphosphorous triamide or the like and anazodicarboxylate such as diethylazodiazodicarboxylate,dimethylazidodicarboxylate, di-t-butylazodicarboxylate, or the like at atemperature of from -78° C. to 25° C. for from 0.5 to 48 hours toprovide 2, which upon reductive debromination in a solvent such asmethanol, methanol-acetic acid, tetrahydrofuran or the like in thepresence of a reducing agent such as zinc-silver couple, zinc-coppercouple, tri-n-butyltin hydride, or the like at a temperature of from 0°C. to 80° C. for from 0.5 to 24 hours yields 3.

Relative to structure 1, 2, and 3, in the above diagram the radical Rmay be any conventional, readily removable carboxyl blocking group suchas benzyl, p-nitrobenzyl, trichloroethyl, methyl, or the like. Thede-blocking reaction is illustrated above, and discussed below.Alternatively, R may be a pharmaceutically acceptable ester moiety, suchas pivaloyloxymethyl, 3-buten-1-yl, (2-methylthio)-ethyl or the like.

The de-blocking procedure may be accomplished by any of a variety ofwell-known procedures such as hydrolysis or hydrogenation. Preferablythe carboxyl blocking group R is removed by hydrogenation in a solventsuch as a loweralkanol, for example, ethanol in the presence of ahydrogenation catalyst such as palladium, platinum or oxides thereofunder 1-40 atmospheres of hydrogen at from 0° to 50° C. for from 1 to 10hours. Salts of the free acid are easily prepared by treatment of thefree acid dissolved in an organic solvent such as ethyl acetate,acetone, chloroform, or the like with an equivalent amount of aninorganic base such as sodium bicarbonate, sodium hydroxide, calciumcarbonate or the like, evaporating the organic solvent and lyophilizingthe aqueous phase.

The products of this invention (I) form a wide variety ofpharmacologically acceptable salts with inorganic and organic bases;these include, for example, metal salts derived from alkali metal oralkaline earth metal hydroxides, carbonates or bicarbonates and saltsderived from primary, secondary or tertiary amines such asmonoalkylamines, dialkylamines, trialkylamines, lower alkanolamines,di-loweralkanolamines, lower alkylenediamines, N,N-diaralkyl loweralkylenediamines, aralkylamines, amino substituted lower alkanols,N,N-di-lower alkylamino substituted lower alkanols, amino-,polyamino-and guanidino-substituted lower alkanoic acids and nitrogencontaining heterocyclic amines. Representative examples include saltsderived from sodium hydroxide, sodium carbonate, sodium bicarbonate,potassium carbonate, potassium hydroxide, calcium carbonate,trimethylamine, triethylamine, piperidine, morpholine, quinine, lysine,protamine, arginine, procaine, ethanolamine, morphine, benzylamine,ethylenediamine, N,N'-dibenzylethylenediamine, diethanolamine,piperazine, dimethylaminoethanol, 2-amino-2-methyl-1-propanol,theophylline, N-methylglucamine and the like.

The compounds of the present invention, I, and salts thereof arevaluable antimicrobial substances which are active against variousgram-positive and gram-negative pathogens. Thus, the free acid andespecially the salts thereof such as amine and metal salts, particularlythe alkali metal and alkaline earth metal salts, are useful bactericidesand can be used for removing susceptible pathogens from dental andmedical equipment, for separating microorganisms, and for therapeuticuse in humans and animals. For this latter purpose pharmacologicallyacceptable salts with inorganic and organic bases such as those known inthe art and used for the administration of penicillins andcephalosporins can be utilized. For example, salts such as alkali metaland alkaline earth metal salts, and primary, secondary and tertiaryamine salts can be used for this purpose. These salts can be combinedwith pharmaceutically acceptable liquid and solid vehicles to formsuitable dosage unit forms such as pills, tablets, capsulessuppositories, syrups, elixirs and the like which can be prepared inaccordance with procedures well known in this art.

The novel compounds are valuable antibiotics active against variousgram-positive and gram-negative bacteria and, accordingly, find utilityin human and veterinary medicine. The compounds of this invention cantherefore be used as antibacterial drugs for treating infections causedby gram-positive or gram-negative bacteria, for example againstStaphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Bacillussubtilis, Salmonella typhosa, Pseudomonas and Bacterium proteus. Theantibacterials of the invention may further be utilized as additives toanimal feedingstuffs, for preserving footstuffs and as disinfectants.For example, they may be employed in aqueous compositions inconcentrations ranging from 0.1 to 100 parts of antibiotic per millionparts of solution in order to destroy and inhibit the growth of harmfulbacteria on medical and dental equipment and as bactericides inindustrial applications, for example in waterbased paints and in thewhite water of paper mills to inhibit the growth of harmful bacteria.

The products of this invention may be used alone or in combination as anactive ingredient in any one of a variety of pharmaceuticalpreparations. These antibiotics and their corresponding salts may beemployed in capsule form or as tablets, powders or liquid solutions oras suspensions or elixirs. They may be administered orally,intravenously or intramuscularly.

The compositions are preferably presented in a form suitable forabsorption by the gastro-intestinal tract. Tablets and capsules for oraladministration may be in unit dose pesentation form, and may containconventional excipients such as binding agents, for example, syrup,acacia, gelatin, sorbitol, tragacanth, or polyvinylpyrrolidone; fillersfor example, lactose, sugar, maize-starch, calcium phosphate, sorbitolor glycine; lubricants, for example, magnesium stearate, talc,polyethylene glycol, silica; disintegrants, for example, potato starchor acceptable wetting agents such as sodium lauryl sulphate. The tabletsmay be coated according to methods well known in the art. Oral liquidpreparations may be in the form of aqueous or oily suspension, solution,emulsions, syrups, elixirs, etc. or may be presented as a dry product,for reconstitution with water or other suitable vehicles before use.Such liquid prepartions may contain conventional additives such assuspending agents, for example, sorbitol syrup, methyl cellulose,glucose/sugar syrup, gelatin, hydroxyethylcellulose, carboxymethylcellulose, aluminum stearate gel or hydrogenated edible oils, forexample almond oil, fractionated coconut oil, oily esters, propyleneglycol, or ethyl alcohol; preservatives, for example methyl or propylp-hydroxybenzoates or sorbic acid. Suppositories will containconventional suppository bases, e.g., cocoa butter or other glyceride.

Compositions for injection may be presented in unit dose form inampules, or in multidose containers with an added preservative. Thecompositions may take such forms as suspensions, solutions, or emulsionsin oil or aqueous vehicles, and may contain formulatory agents such assuspending, stabilizing and/or dispersing agents. Alternatively, theactive ingredient may be in powder form for reconstitution with asuitable vehicle, e.g., sterile, pyrogen-free water, before use.

The compositions may also be prepared in suitable forms for absorptionthrough the mucous membranes of the nose and throat or bronchial tissuesand may conveniently take the form of powder or liquid sprays orinhalants, lozenges, throat paints, etc. For medication of the eyes orears, the preparations may be presented as individual capsules, inliquid or semi-solid form, or may be, used as drops etc. Topicalapplications may be formulated in hydrophobic or hydrophilic bases asointments, creams, lotions, paints, powders, etc.

Also, in addition to a carrier, the instant compositions may includeother ingredients such as stabilizers, binders, antioxidants,preservatives, lubricators, suspending agents, viscosity agents orflavoring agents and the like. In addition, there may also be includedin the composition other active ingredients to provide a broaderspectrum of antibiotic activity.

For veterinary medicine the composition may, for example, be formulatedas an intromammary preparation in either long acting or quick-releasebases.

The dosage to be administered depends to a large extent upon thecondition of the subject being treated and the weight of the host, theroute and frequency of administration, the parenteral route beingpreferred for generalized infections and the oral route for intestinalinfections. In general, a daily oral dosage consists of from about 15 toabout 600 mg. of active ingredient per kg. of body weight of the subjectin one or more applications per day. A preferred daily dosage for adulthumans lies in the range of from about 80 to 120 mg of active ingredientper kg. of body weight.

The instant compositions may be administered in several unit dosageforms as, for example, in solid or liquid orally ingestible dosage form.The compositions per unit dosage, whether liquid or solid may containfrom 0.1% to 99% of active material, the preferred range being fromabout 10-60%. The composition will generally contain from 15 mg. toabout 1500 mg. of the active ingredient; however, in general, it ispreferable to employ a dosage amount in the range of from about 250 mgto 1000 mg. In parenteral administration the unit dosage is usually thepure compound in a slightly acidified sterile water solution or in theform of a soluble powder intended for solution.

The following examples illustrate but do not limit the product, process,compositional or method of treatment aspects of the present invention.All temperatures are in °C.

EXAMPLE I Preparation ofSodium-5-methyl-3-oxo-6-thia-2-azabicyclo[2.2.0]-hexane carboxylate (4)##STR4## Preparation of2-[1-benzyloxycarbonyl-2-methylprop-1-enyl]-4α-bromo-5α-methyl-6-thia-2-azabicyclo[2.2.0]hexane(2)

To a stirred solution of 46.3 mg (0.1 mmol) ofbenzyl-6α-bromo-6β-[1-hydroxyethyl]penicillanate and 78 mg (0.3 mmol)triphenylphosphine in 5 ml. dry tetrahydrofuran at room temperature (25°C.) under a nitrogen atmosphere is added dropwise 36 μl (0.22 mmole) ofneat diethylazodicarboxylate. The resulting mixture is stirred for 20minutes and evaporated under reduced pressure. The residue is purifiedby plate layer chromatography [3 developments φH--CHCl₃ (2:1)] to give13.8 mg (31%) of 2: IR (CHCl₃) 1770 and 1724 cm⁻¹ ; NMR (CDCl₃); δ 1.64(d, J=7 Hz, CH₃), 2.14 (s, CH₃), 2.3 (s, CH₃), 3.94 (qd, J=0.8 and 7.0Hz, H-5), 5.21 (ABq, J=12 Hz, CO₂ CH₂ Ph), 5.28 (d, J=0.8 Hz, H-1), and7.39 (s, ArH); mass spectrum m/e 397, 395 (M⁺) [Calc. for C₁₇ H₁₈ NO₃SBr: 395.0188; Found: 395.0187], 316, 256, 231, 166, 164, 91.

Preparation of2-[1-benzyloxycarbonyl-2-methylprop-1-enyl]-5α-methyl-6-thia-2-azabicyclo[2.2.0]hexane(3)

To a stirred suspension of 53 mg. of zinc-silver couple in 0.4 mlmethanol at room temperature is added in rapid succession 41 mg (0.7mmol) of glacial acetic acid and a solution of 85 mg (0.2 mmol) of 2 in0.5 ml methanol. The mixture is stirred under a nitrogen atmosphere for1.5 hours and is then filtered. The filtrate is diluted with ethylacetate and washed successively with dilute, aqueous hydrochloric acid,aqueous sodium bicarbonate, and saturated sodium chloride. The organicphase is dried with magnesium sulfate, filtered, and evaporated.Purification by plate layer chromatography [2 developments CHCl₃ ]provides 39.2 mg (60%) of 3: IR (CHCl₃) 1754 and 1718 cm⁻¹ ; NMR (CDCl₃)δ 1.64 (d, J=6.5 Hz, CH₃), 2.17 (s, CH₃), 2.28 (s, CH₃), 3.84 (m,SCHCH₃), 3.96 (app. t, J=3 and 4 Hz, H-4), 5.12 (dd, J=1.5 and 4 Hz,H-1), 5.2 (ABq, J=12 Hz, CO₂ CH₂ Ph), and 7.38 (s, ArH); m/e 317 (M⁺).

Preparation of sodium-5α-methyl-6-thia-2-aza-bicyclo[2.2.0]-hexanecarboxylate (4)

A mixture of 30 mg. 10% Pd/C, 2 ml methanol, 0.4 ml deionized water, and0.2 ml. 0.1 N pH 7 phosphate buffer is hydrogenated at room temperatureand 50 psi for 25 minutes. To the reduction mixture is added a solutionof 20 mg (0.06 mmol) of 3 in 0.6 ml methanol. The resulting mixture ishydrogenated at room temperature and 50 psi for 0.5 hour. The catalystis removed by filtration through celite and washed with methanol. Thefiltrate is concentrated under reduced pressure and diluted withdeionized water. The pH of the solution is adjusted to 9.0 with 0.2Maqueous sodium bicarbonate and is thoroughly extracted with ethylacetate. The aqueous phase is then acidified to pH 2.5 with 2.5N aqueoushydrochloric acid and is thoroughly extracted with ethyl acetate. Thecombined extracts are dried (MgSO₄), filtered, and evaporated to providefree acid I.

The free acid is converted to its sodium salt 4 by treating an acetonesolution of I (5 mg) with an equivalent weight of sodium bicarbonatedissolved in water, removing the acetone under reduced pressure, andlyophilizing the remaining aqueous phase.

EXAMPLE II

Preparation of Pharmaceutical Compositions

One such unit dosage form consists in mixing 120 mg. sodium5α-methyl-6-thia-2-azabicyclo[2.2.0]hexane carboxylate with 20 mg. oflactose and 5 mg of magnesium stearate and placing the 145 mg mixtureinto a No. 3 gelatin capsule. Similarly, by employing more of the activeingredient and less lactone, other dosage forms can be put in No. 3gelatin capsules and should it be necessary to mix more than 145 mg ofingredients together, larger capsules such as compressed tablets andpills can also be prepared. The following examples are illustrative ofthe preparation of pharmaceutical formulations:

    ______________________________________                                        TABLET                 PER TABLET                                             ______________________________________                                        Sodium-5α-methyl-6-thia-2-azabicyclo-                                   [2.2.0] hexane carboxylate                                                                           125 mg                                                 Cornstarch, U.S.P.      6 mg                                                  Dicalcium Phosphate    192 mg                                                 Lactose, U.S.P.        190 mg                                                 ______________________________________                                    

The active ingredient is blended with the dicalcium phosphate, lactoseand about half of the cornstarch. The mixture is then granulated with15% cornstarch paste (6 mg) and rough-screened. It is dried at 45° C.and screened again through No. 16 screens. The remaining cornstarch andmagnesium stearate, being the balance, is added and the mixture iscompressed into tablets, approximately 0.5 inch in diameter eachweighing 800 mg.

    ______________________________________                                        PARENTERAL SOLUTION                                                           Ampoule:                                                                      Sodium 5α-methyl-6-thia-2-azabicyclo[2.2.0]-                            hexane carboxylate       500 mg                                               diluent: sterile water for injection                                                                    2 ml                                                OPTHALMIC SOLUTION                                                            Ampoule:                                                                      Sodium 5α-methyl-6-thia-2-azabicyclo[2.2.0]-                            hexane carboxylate       100 mg                                               Hydroxypropylmethyl cellulose                                                                           5 mg                                                Sterile Water             1 ml                                                OPTIC SOLUTION                                                                Ampoule:                                                                      Sodium 5α-methyl-6-thia-2-azabicyclo[2.2.0]-                            hexane carboxylate       100 mg                                               Benzalkonium Chloride     0.1 mg                                              Sterile Water             1 ml                                                TOPICAL OINTMENT                                                              Sodium 5α-methyl-6-thia-2-azabicyclo[2.2.0]-                            hexane carboxylate       100 mg                                               Polyethylene Glycol 4000 U.S.P.                                                                        400 mg                                               Polyethylene Glycol 400 U.S.P.                                                                          10 gram                                             ______________________________________                                    

The active ingredient in the above formulations may be administeredalone or in combination with other biologically active ingredients as,for example, with other antibacterial agents such as lincomycin, apenicillin, streptomycin, novobiocin, gentamicin, neomycin, colistin andkanamycin, or with other therapeutic agents such as probenecid.

What is claimed is:
 1. A compound having the structure: ##STR5## and itspharmaceutically acceptable salts and esters.
 2. An antibioticpharmaceutical composition comprising, in unitary dosage form, atherapeutically effective amount of a compound according to claim 1 anda pharmaceutical carrier therefor.